1. Field of the Invention
The present invention relates generally to coding/decoding technology in a communication system, and in particular, to a coding/decoding apparatus and method for a CDMA (Code Division Multiple Access) mobile communication system using an error correcting code.
2. Description of the Related Art
An IMT-2000 (International Mobile Telecommunication-2000) system, a future CDMA mobile communication system, transmits user data for a voice service, an image service and a data service, along with control data for performing the services. It is important to minimize errors occurring during the transmission of such data in order to improve the quality of the services. To this end, error correcting codes for correcting data bit errors are used to minimize the errors occurring during transmission of the data. Since using the error correcting codes is aimed at minimizing the data bit errors of the transmission data, it is very important to use optimal error correcting codes.
Typically, linear codes are used for the error correcting codes, because it is easy to analyze their performances. Hamming distance distribution for codewords of the error correcting codes serve as a measure indicating the performance of the linear codes. The “Hamming distance” is the consecutive number of non-zero symbols in a codeword. That is, for a certain codeword ‘0111’, the consecutive number of 1's included in the codeword is 3, so that the Hamming distance is 3. The smallest value among the Hamming distance values is called a “minimum distance”, and an increase in the minimum distance of the codeword improves the error correcting performance of the codeword. In other words, the “optimal code” means a code having the optimal error correcting performance.
A paper, An Updated Table of Minimum-Distance Bounds for Binary Linear Codes (A. E. Brouwer and Tom Verhoeff, IEEE Transactions on information Theory, VOL 39, NO. 2, March 1993), discloses an intercode minimum distance, which depends on the input and output values of the binary liner codes and is adapted to generate optimal codes depending on the number of coded symbols generated by encoding input information bits.
The paper discloses a (12,5) linear code for which the number of input information bits is 5 and the number of output coded symbols is 12, and its optimal code has the minimum distance of 4. Therefore, when using the (12,5) linear code, it is necessary to consider both using the optimal code having the minimum distance of 4 and creating the optimal code having the minimum distance of 4, while at the same time, minimizing hardware complexity.
In addition, the paper discloses a (24,6) linear code for which the number of input information bits is 6 and the number of output coded symbols is 24. Its optimal code has the minimum distance of 10. Therefore, when using the (24,6) linear code, it is necessary to consider both using the optimal code having the minimum distance of 10 and creating the optimal code having the minimum distance of 10 while minimizing hardware complexity.